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The emerging fields of 5G and 6G telecommunication networks, Internet of Things, and artificial intelligence have intensified the demand for green nanostructured materials with adjustable and intelligent features that respond to external stimuli. By leveraging the insulator-to-metal transition of VO2 nanoparticles, responsive composite films were developed by integrating these nanoparticles within a biopolymeric network of cationic cellulose nanofibers (CNF+). These films exhibit a reversible change in GHz permittivity upon exposure to thermal or optical stimuli, facilitating dynamic control of their electrical properties. The layered structure of the films further enhances their robustness, featuring a VO2 nanoparticle core encased within CNF+ layers. This design not only strengthens the structure but also significantly boosts light-induced conductivity, particularly in layered variant, underscoring its potential in optoelectronic applications. Simulation studies reveal that the nonuniform, reconfigurable intelligent surface (RIS) of the developed mixed film adeptly manipulates incident electromagnetic waves, making it suitable for 5G/6G wireless signals. Conversely, the layered film serves as a switchable electromagnetic interference (EMI) shield, demonstrating notable differences in shielding efficiency between its hot and cold states. Consequently, CNF+/VO2 composite films designed in this work emerge as a versatile, adaptable platform for intelligent electronics, particularly in the realm of 5G/6G wireless communications.

This paper presents a novel, compact, and high gain metasurface (MS) patch antenna. The antenna structure consists of a slotted square patch in a fractal shape, integrated with a metasurface layer stacked on Taconic RF-30 dielectric material. The individual cells are arranged periodically, creating a 5 x 5-layer configuration. The proposed antenna is designed with physical dimensions of 290 x 290 mm² and achieves a maximum gain of 13.3 dBi at a frequency of 2.2 GHz. Moreover, it achieves a satisfactory minimum reflection coefficient of -10.9 dB. The design process and analysis were performed using the CST MWS simulation software. Based on the performance results obtained from this study, the suggested antenna can be considered suitable for applications in 5G communication.

This work presents a tunable and wideband dual-functional metasurface (DFM) operating in the terahertz regime with highest overlap bandwidth (OBW). The structure consists of a double-split ring resonator and a meandered square ring resonator based on VO2 to achieve reflective cross-polarization conversion and absorption functionalities, respectively. When the phase changing material VO2 is in its metallic state, the metasurface acts as a perfect absorber with a peak absorption of ≥ 90% over the operating band of 2.3–4.01 THz. When VO2 is in its insulating state, the metasurface acts as a reflective cross-polarization converter over a wideband from 1–4.1 THz with high polarization conversion ratio of ≥ 90%. The proposed DFM has a stable response up to 45∘ of incidence in the polarization converter state and 60∘ of angular stability under the absorber state. Further, tunability is achieved by integrating photoconductive silicon and controlling the optical pump intensity in the double-split ring and meandered . square ring resonators. The proposed metasurface finds its applications in security, detection and THz communication systems.

A security system is needed to prevent theft or other criminal acts. One of the implementations of a popular security system today is the Smart Lock System. This study discusses the design of an intelligent lock system using QR Code scanning as a locker key at the Library of the Faculty of Engineering, Universitas Riau. The design of the device system consists of one piece of ESP8266 Node MCU module, one piece of 12V Power Switch Adapter, one piece of AMS 1117 module with 3.3V and 5V output voltages, three pieces of 5V Relays, three pieces of 12V Solenoids. The security system has been improved compared with existing security systems, such as verification for personal data, email notification, and level login to get theft to treat notification. This paper also measured the delay of the device system. Based on measurement results, the average delay obtained is 1.66 seconds.

The continuous wavelet transform (CWT) has been used in radar-based vital signs detection to identify and to remove the motion artifacts from the received radar signals. Since the CWT algorithm is computationally heavy, the processing of this algorithm typically results in long processing time and complex hardware implementation. The algorithm in its standard form typically uses software processing tools and is unable to support high-performance data processing. The aim of this research is to design an optimized CWT algorithm architecture to implement it on Field Programmable Gate Array (FPGA) in order to identify the unwanted movement introduced in the retrieved vital signs signals. The optimization approaches in the new implementation structure are based on utilizing the frequency domain processing, optimizing the required number of operations and implementing parallel processing of independent operations. Our design achieves significant processing speed and logic utilization optimization. It is found that processing the algorithm using our proposed hardware architecture is 48 times faster than processing it using MATLAB. It also achieves an improvement of 58% in speed performance compared to alternative solutions reported in literature. Moreover, efficient resources utilization is achieved and reported. This advanced performance of the proposed design is due to consciously implementing comprehensive approaches of multiple optimization techniques that results in multidimensional improvements. As a result, our achieved design is suitable for utilization in high-performance data processing applications.

The Fifth Generation (5G) communication technology will deliver faster data speeds and support numerous new applications such as virtual and augmented reality. The additional need for a larger number of 5G base stations has sparked widespread public concerns about their possible negative health impacts. This review analyzes the latest research on electromagnetic exposure on humans, with particular attention to its effect on cognitive performance, well-being, physiological parameters, and Electroencephalography (EEG). While most of their results indicated no changes in cognitive function, physiological parameters, or overall well-being, the strength of the EEG alpha wave is noticed to vary depending on various aspects of cognitive functions. However, the available studies have not investigated the health effects resulting from exposure from the 5G mobile phone and base station antennas from 700 MHz to 30 GHz on the cognitive performance, well-being subjective symptoms, human physiological parameters, and EEG of adults. There is a need for such research regarding this current emerging technology. Such studies are significant in determining whether 5G technology is indeed safe for humans.

This paper studies the performance of a 14-element dual-band 5G MIMO antenna with body effect and an antenna selection. The antenna operates in the lower frequency band from 3.10 to 3.85 GHz for 5G bands of LTE 42 and 43, whereas the upper band is from 5.60 to 7.20 GHz for the newly assigned 6 GHz WiFi band. The antenna performance was evaluated in free space and under the effect of human body in three scenarios, namely one-hand, two-hands, and call mode. All resulting envelope correlation coefficients are less than 0.3. On the other hand, the free space efficiency of the antenna elements is between 41 % to 77 % in the lower band and 61 % to 95 % in the upper band. Meanwhile, the efficiency of the elements varies depending on the interaction between each element with the hands and the head, with the least obstructed element efficiency degrading to 8 % relative to free space levels. Due to the body effect, multiplexing efficiency loss varies from 2.68 dB to 5.93 dB and the capacity loss is from 14 % to 38 %. Finally, a selection algorithm is used to assess the performance of the overall antenna when 12, 10 and 8 antenna elements are selected for operation. In free space and with number of elements 12, 10 and 8, the system achieves 91.7 %, 80 % and 67 % from the capacity of the 14-element MIMO antenna, respectively. However, in the vicinity of the body, these values increase to 96.3 %, 85.0 % and 72 % from the capacity of the 14-element MIMO antenna, respectively. This signifies that the less-contributing elements as a result of body blockage can be deselected in order to preserve system resources that these elements consume while contributing less significantly to the performance.

In this paper, the design of a multiband multiple-input multiple-output (MIMO) antenna with frequency and radiation pattern reconfiguration capability in the 5G sub-6 GHz band is presented. Frequency and radiation pattern reconfiguration are enabled on the antenna consisting of two planar inverted-F antenna (PIFA) elements using PIN diodes and DC biasing circuits. At the reflection coefficients of less than −6 dB, both PIFA element 1 and PIFA element 2 achieves triband with bandwidth from 220 MHz to 2330 MHz, ranging from 0.8 GHz to 6 GHz, covering cellular bands for GSM, UMTS, LTE and 5G-NR bands. Moreover, high isolation of at least −10 dB and envelope correlation coefficient with less than 0.3 between ports ensures satisfactory MIMO diversity performance. PIFA elements 1 and 2 have achieved main lobe gain ranging from 1.06 dB to 2.97 dB at their respective resonant frequencies with total efficiencies ranging from 46.2% to 74.5% achieved within the operating bandwidth. This enables a calculated channel capacity of 9.45 to 10.5 bit/s/Hz for PIFA element 1 and 9.56 to 10.23 bit/s/Hz for PIFA element 2, respectively. The percentage of channel capacity achieved over IID capacity for both PIFA elements ranges from 73.71% to 92.8%. Simulated antenna performance parameters agreed well with measurements, and potentially enables reliable and consistent data throughput for 5G mobile terminals.

The next-generation wireless technology that can fulfill such a demand, namely the fifth-generation (5G) technology, should provide 1000 times larger capacity. Moreover, sixth-generation (6G) communication, which represents a significant upgrade from the fifth-generation (5G) network and is anticipated to operate from 100 GHz to 3 THz band, will be required in the years after 2030 due to newly developed data-hungry applications and the greatly expanded wireless network. To meet the ever-growing demands of wireless carriers, an efficient wireless access method that can improve wireless area throughput without expanding bandwidth or cell size is required. Radio Frequency (RF) Orbital Angular Momentum vortex waves (which is now on referred to as OAM waves) to address the concerns mentioned above have attracted much attention in recent years. Due to their orthogonality, different OAM waves of different modes can be multiplexed in the same frequency channel, which can greatly increase the channel capacity. Using the orthogonal modes, a new type of multiple access scheme known as Mode Domain Multiple Access (MDMA) can be used by multiple users using the same frequency channel without additional resources such as frequency and time. As a result, the channel capacity for the next generation wireless communication systems can be enhanced as well as the overall spectrum efficiency can be improved. This review paper begins with an overview of the next generation communication such as 5G communication technology and beyond. This paper first briefly discusses the theory of OAM waves and several methods to generate OAM waves. Various different designs have also been analyzed for their ability to generate OAM waves and discussion on several restrictions and solutions to resolve. Open concerns and development trends are discussed for possible future RF OAM antenna upgrades. This study also proposes that for next generation wireless communication employing OAM, the typically used Uniform Circular Array (UCA) could be paired with the Multiple-Input-Multiple-Output (MIMO) system to improve performance in dense or urban areas for multiusers. In addition, the purity of OAM-modes needs to be considered for efficient utilization of the OAM system for future communications at the radio domain.

This paper presents a triband antenna with a simple design for X-band applications. The proposed antenna is designed based on a patch with a truncated corner slot and complementary split-ring resonators in the ground plane. In this way, the antenna exhibits three operating bands and its resonant frequencies can be controlled independently by changing dimensions of the slot in the patch and the resonator structures in the ground plane. In addition, due to the antiresonant behavior of the complementary split-ring resonator structures, the antenna exhibits a notch-band characteristic at 10.7 GHz. A parametric study is performed to provide a detailed understanding of the independent resonance tuning behavior of the antenna. Both simulated and measured results of the proposed antenna are presented, which are in good agreement. The proposed antenna shows three operating bands in the X-band including (with absolute and relative bandwidths) 9.4–9.7 GHz (300 MHz, 3.14%), 10.3–10.6 GHz (300 MHz, 2.86%), and 11.05–11.32 GHz (297 MHz, 2.66%). In addition to that, a notched band of 10.6–11.05 GHz is introduced to exclude operation in the frequency bands of radiometric observation systems (10.6–10.7 GHz). To the best of our knowledge, this work is unique in its combination of independent tuning of three frequency bands of operation with single-layer implementation in the X-band. Such a structure provides additional degrees of freedom to the antenna design, customizing operation in the required bands while avoiding operation in other bands.

This work presents an efficient design and optimization method based on characteristic mode analysis (CMA) to predict the resonance and gain of wideband antennas made from flexible materials. Known as the even mode combination (EMC) method based on CMA, the forward gain is estimated based on the principle of summing the electric field magnitudes of the first even dominant modes of the antenna. To demonstrate its effectiveness, two compact, flexible planar monopole antennas designed on different materials and two different feeding methods are presented and analyzed. The first planar monopole is designed on Kapton polyimide substrate and fed using a coplanar waveguide to operate from 2 to 5.27 GHz (measured). On the other hand, the second antenna is designed on felt textile and fed using a microstrip line to operate from about 2.99 to 5.57 GHz (measured). Their frequencies are selected to ensure their relevance in operating across several important wireless frequency bands, such as 2.45 GHz, 3.6 GHz, 5.5 GHz, and 5.8 GHz. On the other hand, these antennas are also designed to enable competitive bandwidth and compactness relative to the recent literature. Comparison of the optimized gains and other performance parameters of both structures are in agreement with the optimized results from full wave simulations, which process is less resource-efficient and more iterative.

This paper analyzes a microwave resonator sensor based on a square split-ring resonator operating at 5.122 GHz for permittivity characterization of a material under test (MUT). A single-ring square resonator edge (S-SRR) is coupled with several double-split square ring resonators to form the structure (D-SRR). The function of the S-SRR is to generate a resonant at the center frequency, whereas D-SRRs function as sensors, with their resonant frequency being very sensitive to changes in the MUT’s permittivity. In a traditional S-SRR, a gap emerges between the ring and the feed line to improve the Q-factor, but the loss increases as a result of the mismatched coupling of the feed lines. To provide adequate matching, the microstrip feed line is directly connected to the single-ring resonator in this article. The S-SRR’s operation switches from passband to stopband by generating edge coupling with dual D-SRRs located vertically on both sides of the S-SRR. The proposed sensor was designed, fabricated, and tested to effectively identify the dielectric properties of three MUTs (Taconic-TLY5, Rogers 4003C, and FR4) by measuring the microwave sensor’s resonant frequency. When the MUT is applied to the structure, the measured findings indicate a change in resonance frequency. The primary constraint of the sensor is that it can only be modeled for materials with a permittivity ranging from 1.0 to 5.0. The proposed sensors’ acceptable performance was achieved through simulation and measurement in this paper. Although the simulated and measured resonance frequencies have shifted, mathematical models have been developed to minimize the difference and obtain greater accuracy with a sensitivity of 3.27. Hence, resonance sensors offer a mechanism for characterizing the dielectric characteristics of varied permittivity of solid materials.

This paper presents an active mode subtraction method based on the characteristic mode analysis to estimate the forward directivity based on the difference in modal significance curves. This made the optimization of the antenna gain in the design process to be more efficient. To the best of the authors' knowledge, such method is innovative and proposed in literature for the first time. This method is derived on the basis that the total radiated field of the antenna, and consequently, the directivity is mainly contributed by the excited dominant modes. To demonstrate its effectiveness, three compact, planar, and wearable antennas with increasing complexity will be designed and optimized using this method. The first is a conventional circular patch antenna operating at 5.3 GHz, whereas the second one is a planar loop antenna operating at 3.08 GHz. The third design is a crown-shaped planar antenna (CPA) with a 3 × 3 artificial magnetic conductor (AMC) plane integrated underneath to reduce potential coupling effects from the body. All three antennas are made fully using textiles with the same thicknesses: felt fabric as its substrate and ShieldIt Super as its conductive textile. For all designs, the use of the proposed method, which is validated using the method of moments, has predicted the maximum direction of radiation and its respective gain at the desired frequencies with good accuracy. Besides that, the design of the AMC plane for the CPA is also optimized using CMA prior to the integration with the antenna and a leather wrist strap. Measurements of the final crown-shaped antenna design indicated a good agreement with simulations, with an operating bandwidth of more than 240 MHz, FBR of 15.73 dB and a directional radiation pattern outward from the body.

In this work, the design procedure of a new decoupling network for different antennas is presented for mobile terminals operating in the Sub-1 GHz band (from 0.698 to 0.96 GHz). To evaluate its applicability for different resonant and non-resonant antenna types, two antenna elements have been chosen to be decoupled using the proposed decoupling network: a printed inverted-F antenna and a capacitive coupling element antenna. Simulation and measurement results showed that the decoupling network offer promising improvements in terms of impedance matching, port isolation, envelope correlation coefficient (ECC), and total efficiency. In addition, the antennas are also investigated with the ergodic capacity, multiplexing efficiency, gain, and diversity gain (both calculated using maximal ratio combining technique). Due to the contribution of the decoupling network, the ECC of both types of multiple antennas are less than 0.3, with a 30 % improvement in total efficiency and an inter-element spacing miniaturization of 34 %.

Characteristic modes can be used to solve many radiation and scattering problems involving fully conducting structures. The basic concept is to use eigenvalues and eigenvectors of the characteristic mode equations of a certain topology, and to use these eigenmode currents to control the radiating structure’s behavior. This is accomplished by understanding the overall reflection and radiation characteristics across the operating frequency band. More specifically, characteristic modes are effective for example in determining the best location for the excitation of a radiating structure. In this paper, a comprehensive overview is provided to the different studies and their results obtained for different antennas that are based on the characteristic mode analysis method. A future perspective is given regarding the potential of this method in antenna analysis and design.

This paper presents a hybrid mutual coupling reduction technique applied onto a dual-band textile MIMO antenna for wireless body area network and 5G applications. The MIMO antenna consists of two hexagonal patch antennas, each integrated with a split-ring (SR) and a bar slot to operate in dual-band mode at 2.45 GHz and 3.5 GHz. Each patch is dimensioned at $47.2 \times 31$ mm2. This hybrid technique results in a simple structure, while enabling significant reduction of mutual coupling (MC) between the closely spaced patches (up to $0.1\lambda$ ). This technique combines a line patch and a patch rotation technique, explained as follows. First, a line patch is introduced at an optimized distance to enable operation with a broad impedance bandwidth at both target frequencies. One of the patches is then rotated by 90° at an optimized distance, resulting in a significant MC suppression while maintaining the dual and broad impedance bandwidth. The proposed MIMO antenna is further evaluated under several bending configurations to assess its robustness. A satisfactory agreement between simulated and measured results is observed in both planar and bending conditions. Results show that the MIMO antenna achieves an impedance bandwidth of 4.3 % and 6.79 % in the 2.45 GHz and 3.5 GHz band, respectively. Moreover, very low MC ( $S_{21} < -30$ dB) is achieved, with a low (< 0.002) envelop correlation coefficient, and about 10 dB of diversity gain at both desired frequencies using this technique. Even when bent at an angle of 50° at the $x$ - and $y$ -axes, the antenna bent maintained a realized gain of 1.878 dBi and 4.027 dBi in the lower and upper band, respectively. A robust performance is offered by the antenna against the lossy effects of the human body with good agreements between simulated and measured results.

In this article, a compact printed monopole dual-band antenna using artificial magnetic conductor (AMC)-plane with improved gain and broader bandwidth, applicable for off-body internet of things (IoT) devices is presented. The monopole antenna consists of two C-shaped resonators connected through a U-shaped monopole, parasitic elements, discrete ground circular rings and a co-planar waveguide (CPW) feedline. Each artificial magnetic conductor (AMC) unit cell consists of a slotted circular and a square stubs, designed with two zero-crossing phases for improving the radiation characteristics and to achieve the high gain. The overall size of the proposed AMC-backed antenna is 44.4 mm $\times44.4$ mm $\times1.6$ mm with electrical dimensions of $0.75\lambda _{g}\,\,\times \,\,0.75\lambda _{g}\,\,\times \,\,0.027\lambda _{g}$ . This AMC-backed antenna featured measured bandwidths of 9.6% and 12.4% with improved measured gain values of 4.88 dB and 4.73 dB at 2.45 GHz and 5.8 GHz, respectively. The specific absorption rate (SAR) values are analysed and found to be 1.58 W/kg at 2.45 GHz and 0.9 W/kg at 5.8 GHz. Therefore, the proposed AMC-backed antenna is useful for off-body IoT devices operating at 2.45 and 5.8 GHz industrial, scientific, and medical (ISM) band applications.

Yesterday’s “Big Data” is today’s “data.” As technology advances, new difficulties and new solutions emerge. In recent years, as a result of the development of Internet of Things (IoT) applications, the area of Data Mining has been confronted with the difficulty of analyzing and interpreting data streams in real time and at a high data throughput. This situation is known as the velocity element of big data. The rapid advancement of technology has come with an increased use of social media, computer networks, cloud computing, and the IoT. Experiments in the laboratory also generate a large quantity of data, which must be gathered, handled, and evaluated. This massive amount of data is referred to as “Big Data.” Analysts have seen an upsurge in data including valuable and worthless elements. In extracting usable information, data warehouses struggle to keep up with the rising volume of data collected. This article provides an overview of big data architecture and platforms, tools for data stream processing, and examples of implementations. Streaming computing is the focus of our project, which is building a data stream management system to deliver large-scale, cost-effective big data services. Owing to this study, the feasibility of large-scale data processing for distributed, real-time computing is improved even when the systems are overwhelmed.

A flexible folded-shorted patch (FSP) antenna with dual-band functionality for wearable applications is presented. The proposed antenna is operational at 400 MHz and 2.4 GHz and can be considered compact for the lower operational frequency band (0.13λo × 0.13λo × 0.02λo). Flexible polydimethylsiloxane (PDMS) is used as the substrate due to its relatively low-cost as well as its robustness for wearable applications. A comparison of the fields radiated by the FSP, in terms of the TM010 and TM001 modes are also presented considering the cavity model which is actually related to the two noted operating bands. Equations needed to calculate the beam pattern and directivity for these modes are also derived and their results are compared to commercial full-wave simulations and measurements of a wearable PDMS prototype. An analysis was also performed to characterize the relevant dimensions that are important for independently controlling or tuning the resonant frequencies for these two radiating modes. The proposed antenna can be suitable for robust wearable applications such as military search and rescue operations, emergency response team units, and medical services.

A wearable textile antenna with dual-band and dual-sense characteristics is presented in this work. It operates at the 2.45 GHz band for WBAN and WLAN applications, and at the 1.575 GHz band for Global Positioning System (GPS) applications. An antenna backing based on an artificial magnetic conductor (AMC) plane operating at 2.45 GHz band is introduced to reduce the backward radiation and to improve antenna gain. It consists of a $3\times 3$ array of square patch unit cells, where each unit cell is integrated with four square slits and a square ring. A square-shaped patch is then located on top of the substrate as its radiator. To enable dual-band operation, two corners of this radiator are truncated, with each of the four corners incorporated with a rectangular slit to enable its circular polarization characteristic in the GPS band. Simulation and experimental results are in good agreement and indicate proper antenna operation with linear polarization in the 2.45 GHz band and circular polarization in the 1.575 GHz band, with realized gain of 1.94 dBi and 1.98 dBic, respectively.

The use of the natural materials instead of conventional materials as electromagnetic absorbers promotes environmental sustainability, cost-effectiveness, and ease of accessibility. Furthermore, these materials may also be designed as absorbers and as reinforcements in building materials in a lightweight form. The absorbing ability of composite materials can be customized based on the chosen fillers. Specifically, magnetic and dielectric fillers can be incorporated to improve the absorption of a composite material compared to traditional materials. This work aims to review recent developments of electromagnetic absorbers enabled by nanocomposites, metamaterial and metasurface-based, as well as green composite alternatives. First, the background concepts of electromagnetic wave absorption and reflection will be presented, followed by the assessment techniques in determining electromagnetic properties of absorbing materials. Next, the state-of-the-art absorbers utilizing different materials will be presented and their performances are compared. This review concludes with a special focus on the future perspective of the potential of metamaterial based nanocellulose composites as ultrathin and broadband electromagnetic absorbers.

This paper investigates the performance variation when a different number of antenna elements (AEs) is integrated onto a single MIMO mobile terminal, both in free space and when held in a user hand in data mode. Starting with a minimum of two AEs, this investigation assessed the performance of the MIMO terminal with every additional two AEs (up to 18 AEs) in terms of envelope correlation coefficient (ECC), efficiency, multiplexing efficiency, capacity and maximal ratio combining (MRC). The integrated MIMO antennas are identical and operate between 5 and 6 GHz for 5G applications. Results indicated that ECC increased with the number of AEs. However, ECC remains less than 0.32 for the case of 18 AEs in both free space and with a user hand. Meanwhile, the free space efficiency of about 90 % for the two AEs is observed to decrease with the increasing number of AEs to about 50 % with 18 AEs. However, the efficiency of elements changes with user hand depending on the level of interaction between each element and the hand. Direct blockage of AEs by the hand resulted in efficiencies of as low as 5 %, while at the same time, other AEs retained an efficiency of up to 75 %. At the center frequency of 5.5 GHz, the free space capacity is 11.1, 49.5 and 83.2 bit/s/Hz with two, ten and 18 AEs, respectively. However, the use of the mobile terminal in the proximity of the user hand degraded these levels by 11 % (two AEs), 35 % (10 AEs) and 31 % (18 AEs). Finally, multiplexing efficiency showed that capacity degradation is caused mainly by the degradation of AEs efficiency, whereas the impact of low correlation between AEs is found to be an insignificant factor. In addition to the capacity analysis, gain and diversity gain of the maximal ratio combining technique was also investigated.

In this paper, a miniaturized implantable circularly polarized spiral Planar Inverted-F Antenna (SPIFA) in the UHF (600-800 MHz) band is presented. This antenna is intended for deep implantable devices such as leadless pacemakers and deep brain stimulation (DBS), which facilitates the reception of RF power from an external transmitter. The antenna is electrically small, with a volume of π × 5 m̃m x 5 m̃m × 3.2 m̃m and a diameter of 0.022λ. The performance of the proposed antenna in terms of reflection coefficient, realized gain and axial ratio are assessed when accounting for the effects of operating in different types of human body tissues, different biocompatible materials and different thicknesses and depths of the implanted antenna. Finally, the antenna is prototyped and measured in free space, a phantom model, in a cow's fat and muscle tissues to validate the simulation results, indicating good agreements. A realized gain around -20 dBm is achieved when operating in 50 mm depth in cow's muscle tissue while having electrically very small dimensions compared to implantable antennas reported in the literature.

In this paper, a coplanar waveguide (CPW)-fed patch antenna is fabricated on a layer of metasurface to increase gain. The antenna is fabrication on Roger substrate with a thickness of 0.25 mm, with the overall dimension of the proposed design being 45 × 30 × 0.25 mm3. The size of the patch antenna is 24 × 14 × 0.25 mm3, and the AMC unit cell is 22 × 22 × 0.25 mm3. This metasurface is designed based on the split-ring resonator unit cells forming an array of the artificial magnetic conductor (AMC). Meanwhile, the antenna operation on 3.5 GHz is enabled by etching a split-ring resonator slot on the ground plane with a small gap to enhance antenna gain and improve impedance bandwidth when integrated with a metasurface. This simulation planer monopole antenna is applied for 5G application. The experimenter test is applied for the antenna performance in terms of return loss, gain, and radiation patterns. The operating frequency range with and without MTM is from 3.41 to 3.68 GHz (270 MHz) and 3.37 to 3.55 GHz (180 MHz), respectively, with gain improvements of about 2.7 dB (without MTM) to 6.0 dB (with MTM) at 3.5 GHz. The maximum improvement of the gain is about 42% when integrated with the AMC. The AMC has solved several issues to overcome the typical limitation in conventional antenna design. A circuit model is also proposed to simplify the estimation of the performance of this antenna at the desired frequency band. The proposed design is simulated by CST microwave studio. Finally, the antenna is fabricated and measured. Result comparison between simulations and measurements indicates a good agreement between them.

In this paper, flexible and deployable double-sided linear-to-circular polarizers designed on polydimethylsiloxane are proposed for the first time to the best of our knowledge. ShieldIt textile is used as the conducting element of the two designs based on two different unit cell arrays: a loaded circular patch unit cell or an unloaded circular patch unit cell, both backed by a generic rectangular element on its reverse side. This is in contrast to conventional frequency-selective structure-based linear-to-circular polarizers implemented using rigid substrates, which are multi-layered and requires inter-layer physical spacing. This complicates their implementation using flexible substrates and in a deployable format. Upon implementation of this double-sided polarizer, their final performances are evaluated in terms of the phase difference, conversion efficiency, 3-dB axial ratio (AR), and ellipticity bandwidth (from 40° to 45°). Measurements indicated good agreements with simulations, and both structures exhibited more than 90% of conversion efficiency from 2.34 to 3 GHz (for the loaded circular unit cell) and from 2.36 to 3 GHz (for the unloaded circular unit cell). In terms of ellipticity, a bandwidth of 8.67% is observed for the unloaded design and 13.82% for the loaded design. The unloaded structure exhibited a fractional 3-dB AR bandwidth of 36.36% (from 1.98 to 2.86 GHz) in simulations, and 32.64 % (from 2.00 to 2.78 GHz) when evaluated experimentally. Conversely, the loaded design showed only 12.58%. An equivalent circuit model is proposed and validated via a comparison between the circuit and full-wave simulations. Finally, the performances of these polarizers are also assessed under different bending conditions due to the use of flexible materials, prior to the proposal of a suitable deployment mechanism.

The broadband five-port reflectometer (FPR) is proposed using a triple-ring based technique. The design introduces a tapering in the inter-ring transmission lines (TLs), which provides additional degrees of freedom for optimization and contributes to increased bandwidth. The miniaturization strategy allows incorporating the third ring without significant size increase. In addition, a method for expressing the effective physical dimension of a planar symmetric FPR is also presented in an easily comprehensible way, which can be implemented for other symmetric planar junctions with more than four ports. The proposed design comprises three concentric rings with phase-shifting arrangements between the inter-ring TLs and outer matching arm sections. Inter-ring TLs are shifted by 36° (half factorized value of the inter-port angular distance of 72°) in three different optimizing steps. Tapered TLs have been used between two consecutive rings to achieve very wide bandwidth of at least 88% in simulations and at least 85% in measurements. Curved matching TLs are used in the final design, yielding a compact size of $0.397\lambda _{\mathrm {g}} \times 0.377 \lambda _{\mathrm {g}}$ with 43% reduction in length and 43% in width compared to its non-compact counterpart. Genetic algorithm and quasi-Newton algorithm are used in optimizing the final prototype for operation in the frequency band used for brain microwave imaging. The proposed FPR realized a fractional bandwidth of at least 85% (from 0.96 to 2.38 GHz) with a reflection coefficient below -20 dB and a -6 ± 1 dB transmission coefficient with the required phase shift of ±120° between different ports. The measured results agree well with the simulation. Finally, the overall imaging system setup and image construction algorithm are presented and discussed for possible incorporation with this FPR for brain microwave imaging.

Wearable antennas have gained much attention in recent years due to their attractive features and possibilities in enabling lightweight, flexible, low cost, and portable wireless communication and sensing. Such antennas need to be conformal when used on different parts of the human body, thus need to be implemented using flexible materials and designed in a low profile structure. Ultimately, these antennas need to be capable of operating with minimum degradation in proximity to the human body. Such requirements render the design of wearable antennas challenging, especially when considering aspects such as their size compactness, effects of structural deformation and coupling to the body, and fabrication complexity and accuracy. Despite slight variations in severity according to applications, most of these issues exist in the context of body-worn implementation. This review aims to present different challenges and issues in designing wearable antennas, their material selection, and fabrication techniques. More importantly, recent innovative methods in back radiations reduction techniques, circular polarization (CP) generation methods, dual polarization techniques, and providing additional robustness against environmental effects are first presented. This is followed by a discussion of innovative features and their respective methods in alleviating these issues recently proposed by the scientific community researching in this field.

A planar, low-profile, dual-band and dual-polarized antenna on a semi-flex substrate is proposed in this paper. The antenna is fabricated on Rogers substrate with a thickness of 3.04 mm and sized at 70.4×76.14×3.11 mm3 (0.37λ0 ×0.40λ0×0.016λ0) only. The circular polarization property is enabled in the global navigation satellite system (GNSS) L1/E1 (lower) band by introducing a complementary split ring resonator on the antenna patch. Meanwhile, the antenna operates in the second (upper) 2.45 GHz WLAN band is enabled by etching a U-shaped slot on its ground plane. This simultaneous, dual-band and dual-polarized operation enables the proposed antenna to be applied in the indoor/outdoor wearable application. To isolate the antenna against the influence of the human body, a multiband artificial magnetic conductor (AMC) plane is added on the reverse side of the dual-band radiator. Comparison of the antenna without AMC in free space and when evaluated on the chest of a human body backed by AMC showed improved gain; from 3-5.1 dBi in the lower band, and from 1.53-5.03 dBi in the upper band. Besides that, the front-to-back ratio of the AMC backed monopole antenna also improved from 11-21.88 dB and from 2.5-24.5 dB in the GNSS and WLAN bands, respectively. Next, the specific absorption rate (SAR) of the monopole antenna with and without the AMC plane is assessed. Evaluation results indicate that the maximum SAR value decreased by up to 89.45 % in comparison with the antenna without AMC in the lower band. This indicates the effectiveness of the AMC array in increasing gain and FBR, besides reducing EM absorption in the human body.

Two new flexible, single-sided linear-to-circular polarizers based on the square loop unit cells have been proposed in this work. The first uses a flexible Polydimethylsiloxane (PDMS) substrate, whereas the second polarizer is implemented on a felt textile substrate. Both polarizers uses the same ShieldIt textile to form their conducting elements. The proposed flexible single-layered structure potentially enables the implementation of the polarizer in a deployable format with improved performance consistency and reduced fabrication complexity for size- and weight-constrained applications such as in pico-satellites payloads. The textile-based design offered an improved performance and is advantageous in terms of weight compared to the PDMS-based polarizer. Besides discussing the operation principles and analyzing its surface currents, an equivalent circuit model is also proposed. Measurements of the textile-based polarizer showed satisfactory agreements with its simulated results, featuring a broad 3-dB axial ratio bandwidth of 33.57 %, operating from 1.71 GHz to 2.4 GHz. The bandwidth with at least 90 % of conversion efficiency for this structure is also improved to 47.3 % (from 1.55 GHz to 2.51 GHz), which is better than any other felt-based flexible polarizers in literature. Finally, the performance of the polarizer in different bending conditions is also assessed, indicating improved performance consistency relative to double-sided flexible polarizers.

Angle-of-arrival (AOA) estimation is an important factor in various wireless sensing applications, especially localization systems. This paper proposes a new type of AOA estimation sensor node, known as AOA-estimation system (AES) where the received signal strength indication (RSSI) from multiple radiation pattern reconfigurable (RPR) antennas are used to calculate the AOA. In the proposed framework, three sets of RPR antennas have been used to provide a coverage of 15 regions of radiation patterns at different angles. The salient feature of this RPR-based AOA estimation is the use of Fuzzy Inferences System (FIS) to further enhance the number of estimation points. The introduction of a modified FIS membership function (MF) based on Gaussian function resulted in an improved 85% FIS aggregation percentage between the fuzzy input and output. This later resulted in a low AOA error (of less than 5%) and root-mean-square error (of less than 8°).

This paper presents the assessment of short-term wireless body area network (WBAN) exposure, which is operated at the industrial, scientific, and medical (ISM) band (2.45 GHz) in the vicinity of the human body. The experiment utilizes two popular textile antenna topologies, a planar monopole and a patch antenna as the radiating sources. The objective of this experiment is to investigate whether the exposure from WBAN may influence the physiological parameters (body temperature, blood pressure, and heart rate) and the well-being of the wearer. Counter-balanced, crossover, and the single-blind method was applied in the experimental setup. P-value is the probability value, under the assumption of no effect or no difference (the null hypothesis) of obtaining a result equal to or more extreme than what was actually observed. If P0.05, which failed to reject the null hypothesis (no effect).

In this paper, we present a textile multiple-input–multiple-output (MIMO) antenna designed with a metamaterial inspired reactive impedance surface (RIS) and electromagnetic bandgap (EBG) using viscose-wool felt. Rectangular RIS was used as a reflector to improve the antenna gain and bandwidth to address well known crucial challenges—maintaining gain while reducing mutual coupling in MIMO antennas. The RIS unit cell was designed to achieve inductive impedance at the center frequency of 2.45 GHz with a reflection phase of 177.6°. The improved bandwidth of 170 MHz was achieved by using a square shaped RIS under a rectangular patch antenna, and this also helped to attain an additional gain of 1.29 dBi. When the antenna was implemented as MIMO, a split ring resonator backed by strip line type EBG was used to minimize the mutual coupling between the antenna elements. The EBG offered a sufficient band gap region from 2.37 GHz to 2.63 GHz. Prior to fabrication, bending analysis was carried out to validate the performance of the reflection coefficient (S11) and transmission coefficient (S21). The results of the analysis show that bending conditions have very little impact on antenna performance in terms of S-parameters. The effect of strip line supported SRR-based EBG was further analyzed with the fabricated prototype to clearly show the advantage of the designed EBG towards the mutual coupling reduction. The designed MIMO-RIS-EBG array-based antenna revealed an S21 reduction of −9.8 dB at 2.45 GHz frequency with overall S21 of

A design of a microstrip quad-band BPF with flexibly controlled bandwidth is presented in this paper. Two dual-mode short-circuited SLRs with a common via-hole are proposed, which are utilized to obtain the first and second passband, while the third passband is generated by implementing the second-order half-wavelength coupled-line resonator. Another dual-mode open-circuited SLR can be operated at the fourth passband. The proposed quad-band BPF is centered at 1.80/2.45/3.50/4.90 GHz for DCS/WLAN/WiMAX and 5G applications. By appropriately choosing the lengths of the four sets of resonators, all passbands can be fully varied independently with minimal effect on other passbands. Moreover, the bandwidth of each passband can be flexibly controlled by tuning the coupling parameters. The dimension of the fabricated proposed filter is about 0.12 × 0.20 λg, indicating the compactness of the design, whereas the measurements are in good agreement with the simulated results. The measured S11 are at least 12 dB in the four passbands. The passbands S21 are approximately 0.65, 1.42, 0.78, and 1.20 dB, which exhibit low insertion loss at the passband frequency of the first, second, third, and fourth passband, respectively.

Ultrawideband (UWB) technology can provide short-range, high bandwidth communications at a very low energy consumption level, which is quite attractive for wireless body area networks (WBAN). In such a system, the presence of the human body brings huge challenges for both the design of the wearable antenna and the propagation model. First of all, the coupling between the wearable antenna and the human body should be considered even in the initial steps of the design, in order to be able to deal with both the possibly deteriorating performance of the antenna as a result of the body and the exposure risk for the body. Second, the propagation channel in WBAN is influenced by the continuous movement of the human body, due to the time-varying scattering of the electromagnetic waves. Lots of researchers have been active in this area and some significant progress has been achieved recently. This paper retrospects the latest results in the field of wearable ultrawideband antennas, propagation channels, and their respective application in WBAN systems.

This paper presents a comprehensive review of mobile terminal antenna researches performed in the past seven years and the current challenges related to the user's influence on the performance of fifth generation (5G) terminal antennas. The main challenges for the designing of mobile terminal antennas are to meet the compact size requirements of built-in structures and their multiband capabilities. The antenna design techniques that are used to achieve broader operating bandwidths with smaller antenna dimensions will be first discussed. This is followed by the effects of user interactions with the head/hand for mobile antennas in terms of radiation efficiency and, consequently, the correlation of multiple input multiple output (MIMO) antenna systems. The ultimate aims of this paper are as follows: 1) to highlight the different frequencies of mobile terminal antennas for different applications; 2) to highlight mobile terminal antennas that have been developed for 5G application; 3) to study and discuss the effects of user's hand on 5G mobile terminal antennas; and 4) to discuss the research gap, issues, and challenges in the field of user's effects on mobile terminal antennas for 5G applications. In addition to that, an investigation of the users' hand effects on two MIMO mobile terminal antennas operational in the sub-6-GHz 5G band is presented. This investigation performed using two MIMO antennas is an attempt to formulate guidelines on efficient mobile terminal antenna design in the presence of user's hand in C Band (from 3.4 to 3.6 GHz) and LTE-U Band 46 (from 5.15 to 5.925 GHz).

This paper proposes the design of a reconfigurable circularly polarized textile antenna. The circular polarization feature in the proposed antenna is generated by the edge truncation of a rectangular patch and the incorporation of a slotted ground plane, whilst the frequency reconfigurability feature is realized by slot size modification via the use of three embedded RF p-i-n diode switches. Consequently, the antenna operation can be switched between six frequencies (1.57, 1.67, 1.68, 2.43, 2.50, and 2.55 GHz) depending on the seven switch configurations. The proposed antenna is validated experimentally to be operable within the WBAN, WLAN, and GPS range in a compact and wearable format, with gains of up to 4.8 dBi.

In this paper, a compact textile ultrawideband (UWB) planar monopole antenna loaded with a metamaterial unit cell array (MTMUCA) structure with epsilon-negative (ENG) and near-zero refractive index (NZRI) properties is proposed. The proposed MTMUCA was constructed based on a combination of a rectangular- and a nonagonal-shaped unit cell. The size of the antenna was 0.825 λ0 × 0.75 λ0 × 0.075 λ0, whereas each MTMUCA was sized at 0.312 λ0 × 0.312 λ0, with respect to a free space wavelength of 7.5 GHz. The antenna was fabricated using viscose-wool felt due to its strong metal–polymer adhesion. A naturally available polymer, wool, and a human-made polymer, viscose, that was derived from regenerated cellulose fiber were used in the manufacturing of the adopted viscose-wool felt. The MTMUCA exhibits the characteristics of ENG, with a bandwidth (BW) of 11.68 GHz and an NZRI BW of 8.5 GHz. The MTMUCA was incorporated on the planar monopole to behave as a shunt LC resonator, and its working principles were described using an equivalent circuit. The results indicate a 10 dB impedance fractional bandwidth of 142% (from 2.55 to 15 GHz) in simulations, and 138.84% (from 2.63 to 14.57 GHz) in measurements obtained by the textile UWB antenna. A peak realized gain of 4.84 dBi and 4.4 dBi was achieved in simulations and measurements, respectively. A satisfactory agreement between simulations and experiments was achieved, indicating the potential of the proposed negative index metamaterial-based antenna for microwave applications.

The paper presents the design and investigation of a flexible all-textile antenna operating in the wireless body area network (WBAN) ultrawideband (UWB) specified by the IEEE 802.15.6 standard. The proposed antenna features an innovative and compact UWB radiator on top of the overall structure with a full ground plane on its reverse side. The radiator, which is based on a microstrip patch combined with multiple miniaturization and broadbanding methods, resulted in a simple topology and a compact size of 39 mm×42 mm×3.34 mm (0.51×0.55×0.043λ). In comparison to the literature, the proposed structure is considered to be the most compact microstrip-based textile UWB antenna to date featuring a full ground plane. The choice of the commercial textiles is also made based on cost efficiency, ease of accessibility, and ease of fabrication using simple tools. Meanwhile, the full ground plane enables the antenna operation in the vicinity of the human body with minimal body coupling and radiation towards it, ensuring operational safety. Besides its operation in the mandatory channels of the WBAN-UWB low and high bands, the proposed antenna also operates and preserves its performance in five other optional channels of the high band when placed on the body and under bend conditions of 30° and 60°. The proposed antenna successfully achieved the specific absorption rate below the regulated limit specified by the Federal Communications Commission.

This work presents the design and optimization of an antenna with defected ground structure (DGS) using characteristic mode analysis (CMA) to enhance bandwidth. This DGS is integrated with a rectangular patch with circular meandered rings (RPCMR) in a wearable format fully using textiles for wireless body area network (WBAN) application. For this integration process, both CMA and the method of moments (MoM) were applied using the same electromagnetic simulation software. This work characterizes and estimates the final shape and dimensions of the DGS using the CMA method, aimed at enhancing antenna bandwidth. The optimization of the dimensions and shape of the DGS is simplified, as the influence of the substrates and excitation is first excluded. This optimizes the required time and resources in the design process, in contrast to the conventional optimization approaches made using full wave “trial and error” simulations on a complete antenna structure. To validate the performance of the antenna on the body, the specific absorption rate is studied. Simulated and measured results indicate that the proposed antenna meets the requirements of wideband on-body operation.

An electrically tunable, textile-based metamaterial (MTM) is presented in this work. The proposed MTM unit cell consists of a decagonal-shaped split-ring resonator and a slotted ground plane integrated with RF varactor diodes. The characteristics of the proposed MTM were first studied independently using a single unit cell, prior to different array combinations consisting of 1 × 2, 2 × 1, and 2 × 2 unit cells. Experimental validation was conducted for the fabricated 2 × 2 unit cell array format. The proposed tunable MTM array exhibits tunable left-handed characteristics for both simulation and measurement from 2.71 to 5.51 GHz and provides a tunable transmission coefficient of the MTM. Besides the left-handed properties within the frequency of interest (from 1 to 15 GHz), the proposed MTM also exhibits negative permittivity and permeability from 8.54 to 10.82 GHz and from 10.6 to 13.78 GHz, respectively. The proposed tunable MTM could operate in a dynamic mode using a feedback system for different microwave wearable applications.

Advances in reconfigurable liquid-based reconfigurable antennas are enabling new possibilities to fulfil the requirements of more advanced wireless communication systems. In this review, a comparative analysis of various state-of-the-art concepts and techniques for designing reconfigurable antennas using liquid is presented. First, the electrical properties of different liquids at room temperature commonly used in reconfigurable antennas are identified. This is followed by a discussion of various liquid actuation techniques in enabling high frequency reconfigurability. Next, the liquid-based reconfigurable antennas in literature used to achieve the different types of reconfiguration will be critically reviewed. These include frequency-, polarization-, radiation pattern-, and compound reconfigurability. The current concepts of liquid-based reconfigurable antennas can be classified broadly into three basic approaches: altering the physical (and electrical) dimensions of antennas using liquid; applying liquid-based sections as reactive loads; implementation of liquids as dielectric resonators. Each concept and their design approaches will be examined, outlining their benefits, limitations, and possible future improvements.

Wireless Body Area Network (WBAN) has attracted more and more attention in many sectors of society. As a critical component in these systems, wearable antennas suffer from several serious challenges, e.g., electromagnetic coupling between the human body and the antennas, different physical deformations, and widely varying operating environments, and thus, advanced design methods and techniques are urgently needed to alleviate these limitations. Recent developments have focused on the application of metamaterials in wearable antennas, which is a prospective area and has unique advantages. This article will review the key progress in metamaterial-based antennas for WBAN applications, including wearable antennas involved with composite right/left-handed transmission lines (CRLH TLs), wearable antennas based on metasurfaces, and reconfigurable wearable antennas based on tunable metamaterials. These structures have resulted in improved performance of wearable antennas with minimal effects on the human body, which consequently will result in more reliable wearable communication. In addition, various design methodologies of meta-wearable antennas are summarized, and the applications of wearable antennas by these methods are discussed.

This work reviews design aspects of liquid metal antennas and their corresponding applications. In the age of modern wireless communication technologies, adaptability and versatility have become highly attractive features of any communication device. Compared to traditional conductors like copper, the flow property and lack of elasticity limit of conductive fluids, makes them an ideal alternative for applications demanding mechanically flexible antennas. These fluidic properties also allow innovative antenna fabrication techniques like 3D printing, injecting, or spraying the conductive fluid on rigid/flexible substrates. Such fluids can also be easily manipulated to implement reconfigurability in liquid antennas using methods like micro pumping or electrochemically controlled capillary action as compared to traditional approaches like high-frequency switching. In this work, we discuss attributes of widely used conductive fluids, their novel patterning/fabrication techniques, and their corresponding state-of-the-art applications.

This paper presents a compact circularly polarized (CP) antenna with an integrated higher order harmonic rejection filter. The proposed design operates within the ISM band of 2.32 GHz- 2.63 GHz and is suitable for example for wireless power transfer applications. Asymmetrical truncated edges on a square ring create a defected ground structure to excite the CP property, simultaneously realizing compactness. It offers a 50.5% reduced patch area compared to a conventional design. Novel stubs and slot shapes are integrated in the transmission line to reduce higher (up to the third) order harmonics. The proposed prototype yields a -10 dB reflection coefficient (S11) impedance bandwidth of 12.53%, a 3 dB axial ratio bandwidth of 3.27%, and a gain of 5.64 dBi. Measurements also show good agreement with simulations.

Cube Satellite (CubeSat) technology is an attractive emerging alternative to conventional satellites in radio astronomy, earth observation, weather forecasting, space research, and communications. Its size, however, poses a more challenging restriction on the circuitry and components as they are expected to be closely spaced and very power efficient. One of the main components that will require careful design for CubeSats is their antennas, as they are needed to be lightweight, small in size, and compact or deployable for larger antennas. This paper presents a review of antennas suitable for picosatellite applications. An overview of the applications of picosatellites will first be explained, prior to a discussion on their antenna requirements. Material and antenna topologies which have been used will be subsequently discussed prior to the presentation of several deployable configurations. Finally, a perspective and future research work on CubeSat antennas will be discussed in the conclusion.